The present invention relates to underwater aerators for dissolving oxygen into organic waste water with high efficiencies.
With aerators, it is essential to fully dissolve oxygen into waste water in a tank and to circulate the waste water through the interior of the tank.
Aerators of the mechanical type or air diffusion type have heretofore been used for purifying organic waste waters. Mechanical aerators comprise a drive unit adapted to be positioned above the level of waste water in a purifying tank and an agitator coupled to the drive unit for agitating the waste water at an upper portion of the tank to cause the water to contact air over an increased area by scattering drops of water, thus permitting an increased amount of oxygen to dissolve into the water for aeration. Since the aerator is adapted only for this mode of operation, it is unable to circulate the waste water through the purifying tank, almost failing to aerate the water near the bottom and corners of the tank. Accordingly the purifying tank, if useful, must have a small depth but a large open area, which imposes serious limitations on the installation of the apparatus. Additionally the drive unit disposed above the water level produces a noise and disturbs the environment. In a very cold climate or during winter, the surface of the waste water will freeze. The aerator is then unusable unless the ice is broken, and spattered drops of water will freeze as on the drive unit, rendering the apparatus inoperable for subsequent treatment.
With aerators of the air diffusion type, air is merely supplied to an air diffuser tube provided on the bottom of a waste water purifying tank and therefore will not give off a disturbing noise. However the operation in which the waste water must be agitated and circulated with the air forced out from the diffuser tube requires an air supply unit of large capacity for discharging air at very high pressure. Moreover there is the need to use a purifying tank of large open area to cause the waste water to contact air over an increased area. The aerator nevertheless is unable to fully agitate the waste water despite the use of such large air supply unit and purifying tank; with an insufficient amount of oxygen dissolved into the waste water, the aeration efficiency achieved is low. The aerator has another drawback in that while it is out of operation, suspended solids in the water frequently clog up the air diffuser tube, and extreme difficulties are encountered in remedying this problem and maintaining the apparatus in a proper condition.